Interaction of polypeptides with hair in different reducing environments

Innovation in product development and cosmetic treatments is essential to meet the demands of the hair care industry. This work studied the influence of reducing environments in the interaction of polypeptides (KP peptide, ELP-KP and BSK recombinant proteins and hydrolyzed keratin) with damaged hair, to recover the hair damage. The reducing conditions resulted from thioglycolic acid and thioanisole addition. The small peptide (KP) demonstrated good penetration into the hair and a higher improve in the fibers' mechanical properties without a reducing environment. In opposition, hydrolyzed keratin and BSK, proteins with high molecular weight and rich in cysteine residues, bounded principally to the cuticle and improved the hair mechanical properties mainly under reducing environments. ELP-KP didn't showed any improvement in fibers' mechanical and thermal properties, probably due to the lower percentage of cysteines and their localization into the protein, reducing the interaction with the hair cysteine residues. A thermal study demonstrated that BSK and KP have a greater increase in the keratin alpha-helix denaturation temperature and enthalpy, respectively, demonstrating the polypeptides stabilizing effect on fibers' secondary structure. These results showed that, not only the reducing environment can influence the products final performance, but also the polypeptides' cysteine content and molecular weight.